Late Frasnian Atrypida (Brachiopoda) from the South Urals, South Timan and Kuznetsk Basin (Russia) MARIA A. RZHONSMTSKAYA, BORIS p. MARKOVSKtr T, YULIA A. YUDINA, andELENA V. SOKIRAN Rzhonsnitskaya, M.A., Markovskii, B.P., Yudina, Y.A., & Sokiran E.V. 1998. Late Frasnian Atrypida (Brachiopoda) from the South Urals, South Timan and Kuznetsk Basin (Russia). - Acta Palaeontologica Polonica 43,2,305-344. Late Frasnian AĘpida @rachiopoda) from the South Urals, South Timan and Kuznetsk Basin in Russia (east Laurussian and south Siberian shelf domains in Devonian time) reveal significant geneńc and specific diversĘ in the broadly defined Frasnian-Famen- nian (F-F) bio-crisis time. Eighteen species of aĘpid brachiopods have been recorded, representing 4 subfamilies and 10 genera. The new genus GibberosatrypaMarkovskii & Rzhonsnitskaya, and the new subgenus Spinatrypa (Plicspinatrypa)Rzhonsnitskaya are proposed. Four new species Spinatrypina (Spinatrypina) sosnovkiensis Yudina, Spinar rypa (Plicspinatrypa) rossica Rzhonsnitskaya, Iowatrypa nalivkini Rzhonsnitskaya & Sokiran, and Cartnatina(?) biohermica Yudina are described. The representatives of the Vańatrypinae (including especially conrmon Desquamatia (Desquamatia) alticolifur- mis), Spinatrypinae (Spinatrypina) andAtypinae(Pseudoatrypa,?Costatrypa) arewide- ly distributed in the studied regions. The Pseudogruenewaldtiinae are represented by Iowatrypa artdPseudogruenewaldtla, of which the first is distributed worldwide, where- as the only undoubted species of the second is resfficted to South Timan, and probably represents a localized latest Frasnian descendant of lowatrypa. The decline phase of aĘpid development was controlled by a variety of environmental factors tied to the globalKellwasser events, although it was not directĘ triggered by anoxic conditions. The investigated atrypid brachiopods, which were all confined to lower latitudes, disappeared duńng the F-F mass extinction, independently of their environmental and biogeographic settings. Key words: Brachiopoda, Anypida, biostratigraphy,taxonomy, mass-extinction, Kellwasser Crisis, Frasnian, Famennian, Devonian, Russia. MariaA. Rzhonsnitskaya,Boris P. Markovskii [deceased4thluly, 1966], andElenaV. Sokiran [[email protected]], All-Russian Geological Research Institute (VSE- GEI),74 Srednii Pr., 199026 St.Petersburg, Russia. Yulia A. Yudina [[email protected]], Timan-Pechora Scientific Research Centre, Ukhta,2 Pushkin St.169400 Komi, Russia. Introduction The representativesof the order Atrypida (Brachiopoda)are particularly significant in the contextof the Frasnian-Famennian(F-F) mass extinction,marked by the demiseof this previously abundantshelly benthic group, confined to the tropical latitudesin the Devonian(e.9., Copper 1966a,1986).This groupof Devonianbrachiopods is common in many regions of Russia. Detailed investigationof the faunasfrom the westernslope 306 Atrypida from Russla: RZHONSNTTSKAYA er a/. of theSouth Urals beganin the 1930sby Nalivkin (1931,1941,1951) and Markovskii (1948b).They collecteda rich material,but Markovskii's manuscript(1948a) was not published.It was only in 1989 when some new speciesof the Frasnian atrypids were re-describedand preparedfor posthumouspublication by K. I. Adrianova (Markovskii 1989). The Frasnian atrypids from the Timan Ridge were more extensively studied earlier by Lyashenko (1959, 1913), while those from the Kuznetsk Basin were do- cumentedby Alekse eva (1962) and Rzhonsnitskaya(19 64, I975) . The paper contains a comprehensive systematic description of atrypid brachiopods from the late Frasnian of the threeprincipal Devonian regions of Russia, belonging to differenteast Laurussianand Siberian domains (Fig. 1). The shelly faunaswere exten- siveĘ collected at sęveral stratigraphiclevels on the west slopę of the South Urals, in South Timan, and in the Kuznetsk Basin. The main basis to this study is the large collection madeby B.P. Markovskii from the South Urals (depositedin CMGR Museum, St Petersburg,Russia).only a few taxa,notably spinaĘpinids, are omitteddue to their poor representationin thę materialand/orbad preservation.Special emphasisis paid to therecentĘ established subfamily Pseudogruenewaldtiinae (Rńonsnitskaya et al. 1997)' as well as to documentationof internal characters,which were not adequatelystudied in the most aĘpid species from Russia until now. The stratigraphicdistribution of late Frasnian aĘpid species is discussed in detail in order to identify possible aĘpid occrrrencesin thesurvival (earliestFamennian) phase of this bio-crisis.The atrypid-bear- ing strataspan the Late PąImatolepisrhennna to Palmatolepis lingulfurmisZones in the standardconodont biozonation scale of Ziegler & Sandberg(1989). The authorshipis indicatedin parenthesesin the descriptionof particularregions and taxa. Institutional abbreviations: CMGR - Chernyshev's Museum in St. Petersburg; TPNITch - Timan-PetchoraResearch Geological Exploration at Ukhta. Stratigraphic setting of atrypid-bearing sequences West slope of South Urals (M.A. Rzhonsnitskaya & B.P. Markovskii). - The Frasnian strati- graphy and faunas of the SW Urals were elaborated by Chernyshev (1885) and Nalivkin (1930, I94l) and, in more details, by Markovskii (1948a, b); supplementary data were supplied, among others, by Domratchev et ąl. (1948) and Tiańeva (1961, 1973). The conodont zonation of the Frasnian strata was recentĘ given by Abramova (1992). Late Frasnian sequences in this part of the Urals comprise open marine, relatively deep-water deposits (see Fig. 26), mostly of condensed thicknesses, belonging to goniatite and brachiopod facies. The strata are subdivided into: (1) Mendym horizon (dated as Early P. rhenana Zone), followed by (f) AsĘn horizon (corresponding to undivided Late P. rhenana and P linguifurmis zones), correlated with the Manticoceras intumescens and Crickites expectatus regional goniatite zones, respectively (Domrachev et al. 1948;Ttazheva 1973). The Mendym horizon overlies the siliceous-shaly Domanik suite. The lower part of the Mendym horizon is developed in goniatite facies, composed of grey, partly dolomitized limestones (2-f0 m thick), rich in goniatites, brachiopods, the biva]ve Buchiola, crinoids and, locally, corals; aĘpids are absent. The goniatite facies is succeeded by brachiopod facies in the upper part of the Mendym 'lower horizon (= Cuboides beds' of Markovskii I948a, b; Samsonovo suite of Domrachev et al. 1948). The deposits of the brachiopod facies, f0 to 100-140 m thick, are massive light and reddish-grey limestones, and locally dolomites. The AsĘn horizon overlies the Mendym hońzon 'upper without a break, and light and grey fossiliferous limestones (= Cuboides beds'of Markovskii ACTA PALAEONTOLOGTCA POLONTCA (43) (2) 301 Fig. 1. Location of regions studied against the palaeogeography of the Devonian world (modified from Streel 1986: tig. 4);1 - Timan, 2 - South Urals, 3 - Kuznetsk Basin. I948a, b) are the most characteristiclithology. Bioclastic intercalations,composed mostly of diverse brachiopods,crinoids, corals and bryozoans, are common. In some regions, the massive limestones are laterally replaced by units of darkeą bituminous and locally dolomitized brachiopod-bearing limestones,up to 140 m thick. The overlying Barma formation,4 to 25 m in thickness,is composedof similar light-greymassive limestones with common brachiopod shell beds. The Frasnian versus Famennian age of the Barma succession was discussed by Nalivkin (1931), Markovskii (1948a, b) and Tiazheva (196I, 1973), but conodont faunas argued for an earliest Famennian assignment (Palmatolepis triangularis Zone; see Abramova l99f). South Timan (Y.A. Yudina). - The stratigraphy and brachiopod faunas of South Timan were investigatedby Lyashenko (1959, 1973), Rzhonsnitskaya (1960), Yudina (1994, 1996),Yudina & Lyashenko (1997) and Yudina & Moskalenko (1997). The lower part of the upper Frasnian substage(Vetlasyan suite) is developedin so-called '{Jkhta' facies type, characterizedby a sequenceof marls and argillaceous limestones (see Ftg.27), repre- senting an infill phase of the basin in the Early P. rhenana Zone. The stratigraphically slightly younger lower Sirachoy suite is a shallow shelf facies with rich and diverse faunas, mainly brachio- pods, corals, stromatoporoids, and with oncolites. The upper Sirachoy suite (dated still as Early P rhenana Zone) is dominated by fossiliferous reef carbonates with many stromatoporoids, corals, stromatolites and brachiopods. The lower Liyayel suite, dated as earliest P. rhenana Zone, represents a marly facies deposited on the slope below the Sirachoy reefs. Higher in the sequence,in the Sedyu basin, clays with marly intercalationshave yielded numerous well-preserved brachiopods. The associatedbiota includes stromatoporoids, gastropods and ostracods; oncolites are also present. The stratigraphically younger Yezhavozh and Sedyu reefal limestones, within the large Bolshoi Keran biohermal unit, have also yielded numerous brachiopods from small coquinoid lenses, distributed within the stromatoporoid- algal limestones and secondary dolomites. The overlaying evaporite-carbonatedeposits of the topmost Frasnian in South Timan are without brachiopod faunas, and the F-F transition is poorly documented in these fossil-impoverished se- quences. 308 Atrypidafrom Russia; RZHONSNITSKAYA er a/. Kuznetsk Basin (M.A. Rzhonsnitskaya). - Several facies developed in the late Frasnian and early Famennian of the Kuznetsk Basin area (see Fig 28): (1) shallow open-marine (NW and W borders), passing